An Artificial Gastrocnemius for a Transtibial Prosthesis

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Human walking neuromechanical models show how each muscle works during normal, level-ground walking. They are mainly modeled with clutches and linear springs, and are able to capture dominant normal walking behavior. This suggests to us to use a series-elastic clutch at the knee joint for below-knee amputees. We have developed the powered ankle prosthesis, which generates enough force to enable a user to walk “normally.” However, amputees still have problems at the knee joint due to the lack of gastrocnemius, which works as an ankle-knee flexor and a plantar flexor. We hypothesize that metabolic cost and EMG patterns of an amputee with our powered ankle and virtual gastrocnemius will dramatically improve.

An artificial gastrocnemius for a transtibial prosthesis

A transtibial amputee does not have a functional gastrocnemius muscle, which affects the knee as well as the ankle joint. In this investigation, we developed a transtibial prosthesis comprising an artificial gastrocnemius mechanism as well as a powered ankle-foot device. A pilot study was conducted with a bilateral transtibial amputee walking at a self-selected speed. The trial compared muscle electromyography and metabolic cost data for the amputee while using the active gastrocnemius prosthesis and a conventional Flex-Foot prosthesis. The experimental data showed that the compensation for ankle-foot and gastrocnemius function offered by the active device resulted in a reduced metabolic cost for the amputee participant.